Chapter 14 Cell divisin: 2.3 Cell Cntinuity Learning Objectives 2.3.1 2.3.8 The Cell Cycle, Mitsis, Meisis 1. Explain f the terms cell cntinuity and chrmsme. 2. Differentiate between "haplid" and "diplid" number. 3. Define mitsis and describe the cell activities in the state f nn-divisin (interphase) and divisin (mitsis-with diagrams). 4. Give the primary functin f mitsis in single-celled and multicellular rganisms. 5. Cancer definitin and tw pssible causes. 6. Define "meisis and give the functins. Cntinuity f Life means all life riginates frm ther living things f the same type. Cell Cntinuity means that all cells develp frm pre-existing cells. Bth invlve the ability f cells t survive frm ne generatin t the next. When a new cell is frmed frm an existing ne it is much smaller. It ges thrugh 3 stages: It prduces all necessary materials. It grws t full size. It reprduces t frm new cells. - Cells spend mst f their time in stage ne and tw. Chrmsmes When a cell is nt dividing (interphase) the DNA is present as lng thread-like structures called chrmatin. Chrmsmes are cndensed chrmatin visible in the nucleus during cell divisin. Made f DNA and prtein Each human cell has 46 chrmsmes Each chrmsme cnsists f hundreds/thusands f genes A Gene a shrt sectin f DNA which cntains the instructins fr the frmatin f a prtein. The unit f inheritance. All the genes in an rganism make up its genme. Hmlgus Pairs cnsist f tw chrmsmes that each have genes fr the same features at the same psitins. One chrmsme frm the mther and ne frm the father.
Cell Types Smatic cell a bdy cell; a cell whse genes will nt be passed n t future generatins. Germ cell - a cell that is destined t becme a gamete (egg r sperm); a cell whse genes can be passed n t future generatins. A Cell (2n) - Has tw sets f chrmsmes. i.e.: tw f each type f chrmsme. In humans all bdy (smatic) cells are diplid. - They each have ne set f chrmsmes frm the mther and ne frm the father. 2n = 46 A Haplid Cell (n) - Has ne set f chrmsmes. i.e.: ne f each type f chrmsme in the nucleus. In humans eggs and sperm (germ cells/gametes) are the nly haplid cells. - They have half the chrmsme number. n = 23 Haplid n = 6 2n = 8 Haplid n = 9 The Cell Cycle: Haplid n = 4 n = 8 2n = 12 The Cell Cycle describes the lifecycle f the cell during the time perid between ne cell divisin and the next. The lngest phase (~90%) in the cell cycle is interphase. Interphase is the phase when cells are NOT dividing. It invlves 3 key activities: Rapid Grwth and Metablism Replicatin f DNA (Chrmsme dubling) Prductin f new cell Organelles In rder fr cells t pass n all 46 chrmsmes when they divide they must duplicate r duble each ne prir t divisin. Each arm f the chrmsme is identical and called sister chrmatids. Mitsis: Is the name given t smatic cell divisin. Mitsis is a frm f nuclear divisin in which ne nucleus divides t frm tw nuclei, each with an identical set f chrmsmes.
Once a cell has finished Interphase it enters the 4 stages f mitsis (Prphase, Metaphase, Anaphase, Telphase) 1. Prphase Chrmatin cntracts Chrmsmes becme visible as duble stranded structures Nuclear membrane breaks dwn Spindle fibres frm Nuclelus disappears 2. Metaphase Nuclear membrane breaks dwn cmpletely Chrmsmes line up alng the equatr Spindle fibres attach t each centrmere. 3. Anaphase Spindle fibres cntract The centrmeres break, each chrmsme is pulled apart. Oppsite strands are pulled t each ple f the cell. Identical chrmsmes are pulled t each ple. 4. Telphase Chrmsmes elngate and revert back t chrmatin Spindle fibres break. A nuclear membrane frms arund the chrmsmes. The riginal nucleus has divided int tw identical nuclei. Nuclelus refrms.
Cell divisin fllws immediately after mitsis Cell divisin (cytkinesis) in animal cells: A shallw grve called a cleavage furrw frms. The cleavage furrw becmes deeper until it splits the cell int tw. Cell divisin in plant cells: Small membrane enclsed vesicles cllect at the equatr. These vesicles cntain cellulse t frm cell walls & cell membranes. Vesicles frm a cell plate. Cell walls frm n either side f the cell plate. The space in between the tw cells is called the middle lamella. Functins f Mitsis: In single-celled rganisms e.g. bacteria & ameba, mitsis increases the numbers f individuals (i.e. reprductin cells have identical genes). In multi-celled rganisms mitsis increases the number f cells. Mainly respnsible fr grwth and repair f cells. Cancer: Cancer is a grup f disrders invlving a cell r grup f cells lss f the ability t cntrl the rate f mitsis and cell divisin. They frm a mass f cells called a tumur. Benign tumurs cells stp dividing after sme time e.g. warts, skin tags Malignant tumurs uncntrlled multiplicatin f abnrmal cells They may mve and grw in ther parts f the bdy. Treatment surgery, radiatin (burns ut cancer), chemtherapy (use f chemicals t slw dwn mitsis) Causes carcingens cigarette smke, asbests fibres, uv rays, sme viruses (HPV). Meisis: Meisis is a frm f nuclear divisin in which the daughter nuclei cntain half the number f chrmsmes f the parent nuclei.
When diplid cells divide by meisis, haplid cells are frmed. In humans 46 chrmsmes are halved t 23. 2n = 46 ges t n = 23. Meisis ccurs in the varies and the testes t prduce eggs and sperm (haplid cells). Functins f Meisis: When fertilisatin ccurs, the nucleus f the egg, jins with the nucleus f the sperm. This new cell then divides t frm a zygte and eventually an individual. Fr the new cell t have 46 chrmsmes the egg and sperm can nly have 23 each. It allws fr sexual reprductin withut the numbers f chrmsmes increasing. It allws fr new cmbinatins f genes variatin amngst rganisms. Differences between Mitsis & Meisis: